src: Refactor stack preallocation to be reusable for other resource types

This also eases debugging by making preallocation a self-contained operation, such that one can
easily pinpoint a safe location to interrogate the pool's length and capacity.

This change also appears to reduce the number of libsets necessary to run the launch benchmark from
about 700 back down to 511, suggesting that the old preallocation approach was being optimized out!

Author: solb

src/reusable.rs

@@ -87,6 +87,20 @@ where &'a C: SharedMut<Vec<T>> {
 			builder: builder,
 		}
 	}
+
+	pub fn prealloc(&'a self, count: usize)
+	-> StdResult<(), Option<<&'a C as SharedMut<Vec<T>>>::Error>> {
+		use std::collections::LinkedList;
+		use std::convert::TryInto;
+
+		let swap: LinkedList<StdResult<Reusable<_, _>, _>> = (0..count).map(|_|
+			self.try_into()
+		).collect();
+		for temp in swap {
+			temp?;
+		}
+		Ok(())
+	}
 }
 
 impl<'a, T: Default, C: Default + 'a> Default for Pool<T, fn() -> Option<T>, C>

src/stacks.rs

@@ -10,7 +10,6 @@ use reusable::ReusableSync;
 pub fn alloc_stack() -> ReusableSync<'static, Box<[u8]>> {
 	use compile_assert::assert_sync;
 	use reusable::SyncPool;
-	use std::collections::LinkedList;
 	use std::convert::TryInto;
 	use std::sync::Once;
 
@@ -19,13 +18,8 @@ pub fn alloc_stack() -> ReusableSync<'static, Box<[u8]>> {
 	INIT.call_once(|| {
 		let stacks: fn() -> _ = || Some(vec![0; STACK_SIZE_BYTES].into_boxed_slice());
 		let stacks = SyncPool::new(stacks);
-
-		let prealloc = &stacks;
-		let _: LinkedList<Box<_>> = (0..STACK_N_PREALLOC).map(|_|
-			prealloc.try_into()
-				.expect("libinger: stack allocator lock was poisoned during init")
-		).collect();
-
+		stacks.prealloc(STACK_N_PREALLOC)
+			.expect("libinger: stack allocator lock was poisoned during init");
 		unsafe {
 			STACKS.replace(stacks);
 		}